The present invention relates to an alternator to be driven by an engine of a vehicle such as automobile and, particularly, to an improvement of a cooling system thereof.
FIG. 3 is a cross section of a conventional alternator for vehicle, which is disclosed in Japanese Patent Application Laid-Open No. 178137/1987. In the figure, a reference numeral 1 depicts a rotary shaft on which a pulley 2 is fixedly mounted. A rotor 3 includes a magnetic core 4 having a boss portion fixedly mounted on the rotary shaft 1, which has a plurality of magnetic pole pieces 4a arranged peripherally with fixed space, a support ring 5 of non-magnetic material, which is fixedly attached to an inner periphery of the pole pieces 4a and another magnetic core 6 fixedly attached to the support ring, which has a plurality of magnetic pole pieces 6a arranged peripherally with fixed space and alternatingly with the pole pieces 4a.
An exciter core 7 is fixedly arranged around an outer peripheral portion of the boss portion of the core 4 and an inner peripheral portion of the core 6 with air gaps therebetween. An exciting coil 8 is supported by the core 7. A stator core 9 supports a stator coil 10 in slots thereof.
A front bracket 11 supports rotatably the rotary shaft 1 through a bearing 14 and supports fixedly the stator core 9. The front bracket 11 has an inlet hole 11a for conducting cooling air thereinto and an outlet hole 11b for discharging it after heat exchange.
A rear bracket 12 is connected tightly through an O-ring 18 to the front bracket 11 by bolts (not shown) for fixedly supporting the exciting core 7 and rotatably the rotary shaft 1 through a bearing 15.
A rear end portion of the stator coil 10 is covered liquid-tightly by an enclosure 16 of thermally conductive metal material. A space between the metal enclosure 16 and the stator coil 10 is filled with insulating filler 17. The enclosure 16 is fixedly attached liquid-tightly to the stator core 9 and has a cylindrical protrusion 16a fitted in an annular groove 12a provided in the rear bracket 12 and the liquid-tight sealing is provided by a gasket 19 of a viscose material of silicon group which is provided in the groove.
A coolant inlet tube 13 and a coolant outlet tube (not shown) are provided on the rear bracket 12, to which an inlet hose 13a and a outlet hose are liquid-tightly connected, respectively. An annular passage 23a is formed between an inner peripheral portion of the rear bracket 12 and an outer peripheral portion of the enclosure 16, through which liquid coolant supplied from the inlet tube 13 flows in an arrow direction and is discharged from the outlet tube.
A cooling cover 20 of thermally conductive metal material is liquid-tightly mounted on the rear bracket 12. A branch passage 23b for liquid coolant is defined between the rear bracket and the cooling cover. Liquid coolant from the inlet tube 13 is branched at a branch hole 12c of the rear bracket 12 and branched coolant flows therethrough and, at a return hole (not shown) of the rear bracket 12, joined to a discharge side of the passage 23a and discharged through the outlet tube.
A rectifier 21 for converting a.c. current corresponding to a.c. voltage induced in the stator coil 10 into d.c. current and a voltage regulator 22 are fixedly mounted on the cooling cover 20 through heat sinks 21a and 22a, respectively. The voltage regulator 22 responds to an output voltage of the alternator to control an exciting current to thereby regulate a terminal voltage to a predetermined value. A protective cover 24 is mounted on the rear bracket 12 for providing a mechanical protection to the electric elements.
A fan 25 mounted on the magnetic core 4 of the rotor 3 is to supply cooling air mentioned previously.
A cooling effect of the conventional generator mentioned above is as follows. When the rotary shaft 1 is rotated by the vehicle engine through belt means, the fan 25 is rotated to flow cooling air to the front end portion of the stator coil 10 and the stator core 9 to thereby cooling them.
On the other hand, a portion of low temperature liquid engine coolant flows from the inlet hose 13a through the inlet tube 13 and the passage 23a and cools the rear end portion of the stator coil 10 by heat exchange between the latter and liquid coolant. Further, by heat exchange of coolant flowing that the branch passage 23b, the exciting coil 8, the bearing 15, the rectifier 21 and the voltage regulator 22 are cooled indirectly through the core 7 and, then coolant is returned through the discharge tube and the discharge hose to the engine cooling system.
In the conventional alternator mentioned above, in order to direct the portion of the engine coolant to the passage 23a of the alternator, the inlet hose 13a and the outlet hose must be arranged between the engine and the inlet tube 13 and the outlet tube of the alternator, respectively. Due to the fact that protruded portions such as the inlet tube 13 and the outlet tube must be provided on the outer periphery of the rear bracket of the alternator, a problem arises that they interfere other auxiliary devices of the engine or an engine block itself, so that it is difficult in view of layout of an engine room to mount the alternator on the engine.